My Female Cat Has Suddenly Started Peeing and Pooping anywhere But the Litterbox. What to do?

I bought her a month ago and she was fine, i was also getting her to use the toilet rather than a litterbox.. everything was going fine but now she has suddenly started peeing and pooping anywhere..in washroom floor, my bedroom floor. She was doing fine few days ago even. Any Idea?

AND yes, i bought a male cat and i’ve noticed she started doing this the day she met him. She is 8 months old and my male cat is 13 months old.
I need solutions rather than descriptions. WAITING